History and Shape of DNA Notes for in-class objectives & chapter 11

History For hundreds of years scientists have searched for a molecule that transmits inherited traits from one generation to another 1944- Avery found that DNA stored information

History 1950s-Rosalind Franklin discovered the twisted shape of the molecule

History 1953- Watson and Crick find the molecule has a double helix shape

What is DNA? DNA stands for Deoxyribonucleic Acid DNA is the genetic content of a living cell; the instruction manual for a living organism. DNA contains directions for assembling amino acids into proteins The molecule is subdivided into thousands of genes that each code for a trait

Important definitions Proteins: carry out all structures and functions of a cell. Ex: gene for eye color, nose shape or cystic fibrosis Heredity: The transmission of characteristics from parent to offspring. Genes: A sequence of DNA that codes for a protein and determines a trait

Central Dogma of Molecular Biology DNA RNA Protein

Forms of DNA: Chromatin-the DNA is one long continuous strand of information Chromosomes- the DNA is broken up into tightly wound X-shaped structures and moves around while the cell divides.

Each Chromosome can hold thousands of genes Each person has 46 chromosomes and about 23,000 genes total

Structure of DNA The molecule has a double twist- called a double helix

Subunits of DNA A DNA molecule consists of billions of nucleotides bonded together

Nucleotide Made of 3 parts: Sugar Nitrogen Base Phosphate DNA: Deoxyribose RNA: Ribose Nitrogen Base Purines- Adenine and Guanine Pyrimidines- Thymine and Cytosine Phosphate

DNA is a twisted ladder Outside- a sugar-phosphate backbone Inside- nitrogen containing bases The N-bases are held together by hydrogen bonds (2 nucleotides = base pair)

Chargaff’s Rule Adenine always bonds to Thymine, Cytosine always bonds to Guanine Number of A = Number of T Number of C = Number of G

Function of DNA Control of cellular activities: DNA carries the code for assembling enzymes and the other proteins that function in the cell’s metabolism. Replication: DNA replicates itself so that its genetic information is passed on. The genetic information lies in the sequence of the base pairs.

Steps of Replication Unwind Unzip Insert Proofread

DNA Replication DNA replication: the DNA strand “unzips” the weak hydrogen bond comes undone and the base pairs separate.

Insert After the DNA molecule opens up, new nucleotides are brought in and match up to their complimentary base. (A-T, C-G) http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html

Proofreading The nucleus has enzymes that “read” through the molecule looking for mistakes. If one is found, the molecule cuts out the incorrect nucleotide and replaces it. Even with this molecule, sometimes a mistake is made, causing a change.

Something old something new The process is semi-conservative; each new molecule has one of the old strands and one of the new strands.

Modern DNA Research Dolly the sheep and cloning. britannica.com

Modern DNA Research Can we clone a T-rex? www.pbs.org/wgbh/nova/nature/t-rex-blood.html